1. Field of the Invention
The invention relates to the field thick-film circuits on ceramic substrates, and more particularly, to thick-film circuits having conductor paths on opposite sides of a ceramic substrate which are interconnected by through-contacts in the substrate. The invention further relates to technology for producing substrate through contacts.
2. Prior Art
Thick-film circuits having a through-contact arrangement require particular care during manufacture. The walls of the connecting holes, or so-called through-holes, in the ceramic substrate of a thick film circuit may be wetted with high viscosity metal dispersions. After heating, such dispersions produce a conductive path extending through such so wetted through-holes which interconnect, conductor paths on opposite sides of the ceramic substrate. In certain present-day thick-film technology, the through holes are exposed to a vaporized material so that a conductive film is deposited on the entire hole wall. Metal pins are then soldered into the holes.
German Auslegeschrift 1,590,345 discloses a technique wherein copper pins which are coated with a brazing solder are placed in through-holes and are then raised to a sufficiently high temperature, by a passing a current pulse through the pins so that the brazing solder melts while the material forming the conductor paths does not. However, this procedure is expensive for manufacture of sandwich circuits (i.e. circuits having conductor paths on opposite sides of a substrate), since the procedure for establishing through-contacts differs from that employed to produce the conductor paths.
Also in the prior art, through-holes in ceramic substrates have been filled with conventional conductor path pastes of the screen printing type and then sintered. However, the shrinkage of such pastes during the sintering or heat treatment is of such magnitude that electrical connection through the resulting through-contacts in such filled holes often ruptures. Accordingly, this technique is not reliable for mass production of thick-film circuits.